The introduction of West Nile virus (WNV) in to the western hemisphere in 1999 and dramatic increase in both the rate and severity of disease in humans during subsequent transmission seasons, has resulted in its classification as an emerging pathogen of significant public health concern. In areas of Asia, the Middle East and Africa where WNV has been endemic for many years, infections are generally asymptomatic or associated with a mild childhood febrile illness. Recent WNV epidemics in developed countries in Europe and the United States have been associated with significantly higher rates of morbidity and mortality, indicating the emergence of a more pathogenic variant of the virus. Since its introduction into the United States WNV has rapidly spread and has now been detected in nearly every state in the continental U.S.A. The molecular mechanisms for the increase in pathogenesis of WNV are currently unknown but are likely to include novel virus-host interactions that allow the virus to overcome or evade the host innate and/or adaptive immune response. The goal of this research proposal is to define the interactions between a pathogenic WNV isolate and the host innate intracellular response. This proposal is designed to investigate the influence of the host interferon regulatory factor 3 (IRF-3), a central component of the host acute antiviral response, on WNV replication and pathogenesis. Two objectives have been utlined; 1) define the mechanism of IRF-3 signaling by WNV, and 2) define the effect of the IRF-3 pathway upon WNV replication. A more complete understanding of the innate intracellular response to WNV will aid in the development of novel therapeutic approaches to combat WNV infections. [unreadable] [unreadable]